1. Field of the Invention
The present invention relates to plasma processing apparatuses, and more particularly, to a plasma processing apparatus having a matching circuit between a high-frequency power source and a plasma electrode of the plasma processing apparatus.
The present invention also relates to plasma processing apparatuses, matching boxes, and feeders, and more particularly, to a matching box for intervening between a high-frequency power source and a plasma electrode of a plasma processing apparatus, a feeder for supplying high-frequency electric power from the matching box to the plasma electrode, and the plasma processing apparatus.
2. Description of the Related Art
There has been conventionally known a plasma processing apparatus shown in FIG. 11.
High-frequency electric power is supplied from a high-frequency power source 1 to a plasma excitation electrode 4 with a feeder 3 through a matching box 2 which is formed of a housing 21 made from an electrically conductive member and which accommodates a matching circuit in its inside.
Below the plasma excitation electrode 4, a shower plate 5 provided with a number of holes 7 is formed. Between the plasma excitation electrode 4 and the shower plate 5, there is formed a space 6. A gas feeding tube 17 is provided for the space 6. Gas fed through the gas feeding tube 17 is supplied through the holes 7 of the shower plate 5 to a chamber formed of a chamber wall 10. An insulating member 9 insulates the chamber wall 10 from the plasma excitation electrode 4.
In the chamber, a wafer susceptor 8 which also serves as a plasma excitation electrode and on which a substrate 16 is placed is provided. A susceptor shield 12 is provided therearound. The wafer susceptor 8 and the susceptor shield 12 are made movable up and down by bellows 11 so that the distance between the plasma excitation electrodes 4 and 8 can be adjusted.
The wafer susceptor 8 is connected to a second high-frequency power source 15 through a matching circuit accommodated into a matching box 14.
The matching box 2 is provided with a matching circuit shown in FIG. 12. The state of plasma excited in the chamber varies according to processing conditions such as the type of gas and pressure. Since the impedance thereof changes accordingly during discharge, an impedance between the high-frequency power source 1 and the plasma excitation electrode 4 is adjusted by the matching circuit such that a reflection wave of the output of a high-frequency wave applied is the minimum, in order to adjust plasma discharge. A tuning capacitor 24 is used for a part of this adjustment.
In the circuit shown in FIG. 12, a coil 23 and the tuning capacitor 24 are provided in series between the high-frequency power source 1 and the feeder 3. Another load capacitor 22 is connected to the high-frequency power source 1 and one end of the capacitor is grounded. The feeder 3 is usually formed of silver-plated copper 50 to 100 mm wide, 0.5 mm thick, and 100 to 300 mm long. The feeder 3 is screwed on the plasma excitation electrode 4.
In the matching circuit, the capacitance of the tuning capacitor 24 is adjusted to adjust the impedance between the high-frequency power source 1 and the plasma excitation electrode 4.
The inventor of the present invention examined the conventional plasma processing apparatus in detail and found, however, that power consumption efficiency (the rate of a power consumed in plasma to electric power supplied from the high-frequency power source 1 to the plasma excitation electrode 4) is not necessarily satisfactory, and the power consumption efficiency largely decreases as a capacitance between the plasma excitation electrode 4 and the chamber wall 10 of the plasma processing apparatus increases, as shown in FIG. 5.
The power consumption efficiency was examined as follows:
1. Change the chamber wall of the plasma processing apparatus to an equivalent circuit formed of a lumped-constant circuit. PA1 2. Measure the impedance of each component of the chamber with the use of an impedance analyzer to determine the constant of each circuit. PA1 3. Obtain the impedance of the whole chamber during discharge from the fact that the impedance of the whole chamber during discharge is complex conjugate with the impedance of the matching box to which a dummy load of 50 .OMEGA. is attached at the input side. PA1 4. Assuming that a plasma space is a series circuit of a resistor R and a capacitor C, calculate the constant of each component from the values obtained from items 2 and 3. PA1 5. Based on the equivalent circuit model during discharge obtained from the above method, perform circuit calculation to obtain the power consumption efficiency. PA1 1. Change the chamber wall of the plasma processing apparatus to an equivalent circuit formed of a lumped-constant circuit. PA1 2. Measure the impedance of each component of the chamber with the use of an impedance analyzer to determine the constant of each circuit. PA1 3. Obtain the impedance of the whole chamber during discharge from the fact that the impedance of the whole chamber during discharge is complex conjugate with the impedance of the matching box to which a dummy load of 50 .OMEGA. is attached at the input side. PA1 4. Assuming that a plasma space is a series circuit of a resistor R and a capacitor C, calculate the constant of each component from the values obtained from items 2 and 3. PA1 5. Based on the equivalent circuit model during discharge obtained from the above method, perform circuit calculation to obtain the power consumption efficiency.
As described above, in the conventional plasma processing apparatus, a film forming speed is low due to a low power consumption efficiency. It is difficult to form an insulation film having a larger dielectric strength.
The inventor of the present invention sought out the reason for a low power consumption efficiency, and found that the feeder 3 might affect the efficiency. From various experiments based on this finding, the inventor of the present invention then found the power consumption efficiency can be increased by reducing the resistance of the inductance of the feeder to one hundredth, and has made the present invention.
There is also conventionally known a plasma processing apparatus shown in FIG. 18.
In the conventional plasma processing apparatus, a matching circuit intervenes between a high-frequency power source 101 and a plasma excitation electrode 104. The matching circuit is used for obtaining impedance matching between the high-frequency power source 101 and the plasma excitation electrode 104.
High-frequency electric power is supplied from the high-frequency power source 101 to the plasma excitation electrode 104 by a feeder 103.
The matching circuit and the feeder 103 are accommodated into a matching box 102 formed of a housing 121 made from an electrically conductive member.
Below the plasma excitation electrode 104, a shower plate 105 provided with a number of holes 107 is formed. Between the plasma excitation electrode 104 and the shower plate 105, there is formed a space 106. A gas feeding tube 117 is provided for the space 106. Gas fed through the gas feeding tube 117 is supplied through the holes 107 of the shower plate 105 to a chamber formed of a chamber wall 110. An insulating member 109 insulates the chamber wall 110 from the plasma excitation electrode 104. An exhausting system is omitted in the figure.
In the chamber, a wafer susceptor 108 which also serves as a plasma excitation electrode and on which a substrate 116 is placed is provided. A susceptor shield 112 is provided therearound. The wafer susceptor 108 and the susceptor shield 112 are made movable up and down by bellows 111 so that the distance between the plasma excitation electrodes 104 and 108 can be adjusted.
The wafer susceptor 108 is connected to a second high-frequency power source 115 through a matching circuit accommodated into a matching box 114.
FIG. 19 shows another conventional plasma processing apparatus.
In the plasma processing apparatus shown in FIG. 19, a shower plate is not used. A feeder 103 is disposed outside a matching box 102. In other words, a plasma excitation electrode 104 and the feeder 103 connected to the plasma excitation electrode 104 are accommodated into a plasma processing chamber. The other configurations are the same as those of the plasma processing apparatus shown in FIG. 18.
In either plasma processing apparatus, the state of plasma excited in the chamber varies according to processing conditions such as the type of gas and pressure. Since the impedance thereof changes accordingly during discharge, an impedance between the high-frequency power source 101 and the plasma excitation electrode 104 is adjusted by the matching circuit such that a reflection wave of the output of a high-frequency wave applied is the minimum, in order to adjust plasma discharge. A tuning capacitor 124 is used for a part of this adjustment.
In the circuits shown in FIGS. 18 and 19, a coil 123 and the tuning capacitor 124 are provided in series between the high-frequency power source 101 and the feeder 103. Another load capacitor 122 is connected to the high-frequency power source 101 and one end of the capacitor is grounded. The feeder 103 is usually formed of silver-plated copper 50 to 100 mm wide, 0.5 mm thick, and 100 to 300 mm long. The feeder 103 is screwed on the plasma excitation electrode 104.
In the matching circuit, the capacitance of the tuning capacitor 124 is adjusted to adjust the impedance between the high-frequency power source 101 and the plasma excitation electrode 104.
The inventor of the present invention examined the conventional plasma processing apparatus in detail and found, however, that power consumption efficiency (the rate of a power consumed in plasma to electric power supplied from the high-frequency power source 101 to the plasma excitation electrode 104) is not necessarily satisfactory, and the power consumption efficiency largely decreases as a capacitance between the plasma excitation electrode 104 and the chamber wall 110 of the plasma processing apparatus increases.
The power consumption efficiency was examined as follows:
As described above, in the conventional plasma processing apparatuses, a film forming speed is low due to a low power consumption efficiency. It is difficult to form an insulation film having a larger dielectric strength.
The inventor of the present invention sought out the reason for a low power consumption efficiency, and found the following.
In the conventional plasma processing apparatus, high-frequency electric power is supplied from the high-frequency power source 101 to the plasma excitation electrode (cathode electrode) 104 through a coaxial cable, the matching circuit, and the feeder 103. On the other hand, a high-frequency current flows into the plasma space through the components above, and then to an RF power source ground through another electrode (susceptor electrode) 108, the bellows 111, the chamber wall 110, and the housing chassis of the matching box.
Since the feeder 103 is parallel to the housing 121 of the matching box 102 which encloses the feeder 103 in the conventional plasma processing apparatus, the current flows parallel routes, the feeder 103 and the housing 121 of the matching box 102, in the go path and the return path to cause an increase of mutual inductance. As a result, it leads to a decrease in power consumption efficiency, and then a reduce in the film forming speed or a deterioration of film quality. The effect of the mutual inductance becomes large as the substrate 116 is extended. This means the effect is larger as the distance between the feeder 103 and the housing of the matching box 102 becomes longer. When the substrate is 40 to 50 cm long, the effect appears noticeably.
The inventor of the present invention first found the above phenomenon, which includes an issue to be solved.